Top up a validator
You may need to top up your validator's balance for two important reasons. If your validator's effective balance is below 32 Tokio ETH you won't be earning your full staker rewards. And if it drops as low as 16 Tokio ETH the system will eject your validator.
32 Tokio ETH is the maximum effective validator balance. This means you won't earn more rewards if your validator's balance goes above 32. However you will earn less if it dips below 32. More on effective balance